Mass spectrometry refers to an analysis method that separates and detects compounds by different mass-to-charge ratios (m/z) to implement component and structure identification. The mass spectrometry technique has become increasingly prominent in the field of bioanalysis due to its high specificity and sensitivity. Bio-mass spectrometry (Bio-MS) is a mass spectrometry technique applied to analyze biomolecules, which is widely applied in protein and polypeptide researches such as relative molecular mass determination of protein, peptide mapping determination, peptide sequence determination technique, assignment of sulfhydryl group and disulfide bond, posttranslational modification of protein, quantitative proteome analysis, protein-protein interaction research, and the like. Moreover, the bio-mass spectrometry is also applied to such fields as polysaccharose structure determination, oligonucleotide and nucleic acid analysis, microorganism identification, medicament research and development and the like.
With the development of the mass spectrometry technique, its related manners of ionization change rapidly. A bipolar ionization method is developed by many researchers on the basis of the predecessors, which can ionize samples to form positive and negative ions. Huang [1, 2] et al make improvement on the basis of a nano-ESI source, and obtain bipolar ions of the samples through a manner of pulsed high voltage induction. Nishant Chetwani [3, 4] et al also conduct similar studies, and develop a novel high frequency alternating current field ESI source, which can obtain bipolar ions on the basis of different modes. Usually, two different modes based on positive and negative ion are employed to detect the bipolar ions separately. On the other hand, there are also researchers devoting to developing a method of simultaneously detecting bipolar ions: Chen. [5] et al develop a bipolar Taylor cone-based method for synchronously detecting bipolar ions; and Tsai [6] et al develop a bipolar time of flight detector (TOF) based method for detecting bipolar ions and apply relevant patents. Generally, in prior methods, the positive and negative ions are separately detected through using two sets of mass spectrometry/mass analyzers; or through twice mass spectrometry analysis by using one set of mass spectrometry/mass analyzer, where one analysis is for analyzing the positive ions and another analysis is for analyzing the negative ions. In current mode of processing, positive ion mode detection and negative ion mode detection are separately performed by employing different operation parameters, and subsequent detection such as tandem mass spectrometry (also referred to as “MS/MS” hereinbelow) and the like is continuously performed after one polar ion is excluded, which increases the sample consumption and reduces the detection efficiency.